The present development relates to a golf ball, and more particularly, to a golf ball winding apparatus with low combined rotary inertia.
At the present time, wound golf balls remain the preferred golf ball of the more advanced player due to spin and feel characteristics. Wound golf balls typically have either a spherical solid rubber or fluid-filled center around which many yards of a stretched elastic thread are wound forming a wound core. The wound core is then covered with a durable cover material, such as a SURLYN(copyright), which is a trademark for an ionomer resin produced by DuPont de Nemours and Company, or similar material or a softer cover, such as Balata or polyurethane. Wound balls are generally softer and provide more spin, which enables a skilled golfer to have more control over the ball""s flight and position. Particularly, with approach shots onto the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.
The threads wound about the center of the golf ball are usually stretched as tightly as possible without subjecting them to unnecessary incidents of breakage. The reason for this is that the tighter the threads are wound, the more lively the ball. The consequence of this is a relatively high compression for the ball and a relatively high initial velocity.
The threads wound about golf balls frequently contain weak points because of impurities and other imperfections. Because of this, most manufacturers of wound golf balls do not try to wind using the maximum tension or maximum elongation of a thread. Additionally, most manufacturers do not generally use below 85% of the maximum elongation.
From time to time thread breakages will occur even when using a winding tension that produces less than maximum elongation. When a thread breaks during manufacturing, if the winding machine does not lose control of the free end of the thread, the machine needs to be restarted. However, if the winding machine loses control of the free end of the thread, an operator must manually re-thread the machine and restart the operation. Both of these situations decrease production, and thus are undesirable.
However, when such breakages occur during play due to impact of a club face with a ball, they can result in substantially deleterious effects. There can be a substantial loss in velocity of the ball, in the ball deviating from its line of flight, and/or in the ball becoming substantially non-spherical. Such results are undesirable.
Many different apparatuses and methods for winding golf balls exist. Prior art methods utilize power, guide, and brake rollers to feed, orient and tension thread as it is applied to a golf ball center. Prior art winding technology cannot wind threads with low breaking tension in a production environment because the threads break too often. Thread tension varies during the winding procedure, where the initial or start-up tension is typically different than the running tension of the thread during winding and thread breakages can occur throughout the winding procedure.
It is known that a high percentage of thread breaks occur during the initial start-up of winding. During initial start-up, a thread goes from no elongation to a very high elongation over a short period of time. Under such conditions, the thread is much more likely to break. One solution which has been employed is to substantially reduce the tension applied to the thread during the initial stages of winding. Because of the reduced tension, irregularities in the thread are less likely to cause a break in the thread. Furthermore, the reduced initial tension of winding usually results in an overall reduction in breakage of the thread during the entire winding process. It still remains possible that low breaking tension threads will break even if wound at a lower initial tension. One way to wind these types of threads is to wind them slowly. However, winding at these slow speeds is unacceptable in a production environment, where winding time must be minimized.
The prior art rollers and accompanying bearings and shafts typically have high rotational inertia which can impart an initial tension on the thread during start-up greater than the breaking tension. A significant portion of thread tension during start-up is due to inertial forces that are the product of rotational acceleration and rotary inertia. Essentially, high inertia leads to high start-up tension and failure of low breaking tension thread. The initial acceleration of the rollers and shafts can be reduced to prevent thread fracture but slow production rates and poor tension control results. Further complicating matters is the fact that when initiating ball winding, these rollers and shafts typically must accelerate up to winding velocity in less than 5 seconds in order to achieve satisfactory manufacturing results.
Thread breakage can also occur when additional tension is applied to the thread during the winding process. Initially, the majority of the tension is due to the rotational inertia of the rollers as they start from rest and accelerate up to winding speeds. Once winding speed is reached, the tension applied to the thread is increased due to differential rotating velocities of the rollers that the thread traverses, or other tensioning devices which actively tension the thread. The thread will break if the additional tension applied is greater than the breaking tension of the thread.
Prior art apparatuses use frictional brake systems and controlled differential drive systems to apply additional tension to the thread during winding. These systems have wearing parts and commonly need frequent calibration and adjustment due to wear and environmental variations such as those caused by lubricants. Winding at low tension puts a greater premium on the repeatability of the systems and the ability to maintain consistent torque, therefore making it more critical that the systems are properly calibrated. Even when properly calibrated, these systems result in poor tension control at slow winding rates and therefore create golf balls with less uniform thread tension than is desired. Also, prior art winding machines that rely on differential drive systems to induce tension require substantial thread elongation to effect tension control and are costly. Furthermore, these systems present a complex control problem during the start-up phase where desired tension may not be attained instantaneously, and if they are engaged during the initial start-up winding process, additional inertia is added to the overall apparatus, making it more likely for a low breaking tension thread to break.
Therefore, it would be advantageous to provide an apparatus for winding threads with low breaking tension at speeds that are acceptable in a production environment.
The present invention is directed to a winding apparatus for winding a thread on a golf ball center. The apparatus comprises a plurality of rollers supported for rotation and guiding the thread to a golf ball center winding station. The sum of the rotational inertias of all rotating members (i.e., rollers, shafts, and bearings) is low and less than about 3000 or more preferably less than about 1500 grams-cm2.
In one embodiment, the sum of the rotational inertias of the rotating members is less than about 800 grams-cm2. In another embodiment, the sum of the rotational inertias of the rotating members is less than about 200 grams-cm2.
In yet another embodiment, the plurality of rotating members includes at least one tension roller for elongating the thread. In one embodiment, the tension rollers are made of a material with a density less than about 8 g/cm3. The tension rollers can be less than about 4.0 inches in diameter and less than about 0.5 inches thick. At least one tensioning device is operatively connected with one of the tension rollers for adjusting the tension roller. In one embodiment, the tensioning device is a frictional brake. In another embodiment, the tensioning device is a magnetic brake. The magnetic brake can include a permanent magnet or an electro-magnet.
In another embodiment, the tensioning device comprises a second roller adjacent the tension roller configured to elongate the thread between the tension roller and second roller, and the tension roller is rotated at a different speed than the second roller to elongate the thread.
In yet another embodiment, the rotating members further include a plurality of idler rollers. In one embodiment, the idler rollers are made of a material with a density less than about 3 g/cm3. The idler rollers can be less than about 1.5 inches in diameter and less than about 0.5 inches thick. In another embodiment, the rotating members further include a sensing roller.
In addition, the present invention is directed to a winding apparatus for winding a thread on a golf ball center. The apparatus comprises a golf ball center winding station for winding a golf ball center, and a plurality of rotating members spaced from the winding station and supported for rotation and for guiding the thread to the winding station and for tensioning the thread. The rotating members include at least one tension roller and a tensioning device operatively associated with at least one tension roller. The tensioning device includes a magnetic brake that applies a non-frictional torque to at least one tension roller.
The present invention is also directed to a method of winding a golf ball comprising the steps of: providing a golf ball center; winding a thread onto a golf ball center over at least one roller; applying tension to the thread before winding onto the center; and changing the tension by applying a magnetically induced torque to at least one roller such that the torque is non-frictional with respect to the associated roller.
In one embodiment, the step of changing the tension further includes using a magnetic brake, which can include either a permanent magnet or an electro-magnet. In another embodiment, the step of applying tension further includes providing a first brake and a second brake an the first break is always operative and the second brake is selectively operative. In another embodiment, the thread has a break tension below 800 grams.